A number of different technologies exist in the finger touch/touch pad area, but most of them have the drawback that the actual pad is vulnerable and easily breaks.
Touch pads in general are described in e.g. U.S. Pat. Nos. 4,346,376, 4,484,179, 4,688,933, 5,945,981, and 6,122,394, as well as U.S. Pat. Nos. 2003/0048257 and 2003/0052257.